This invention relates, in general, to electroluminescent systems, and more specifically, to an electroluminescent system applied in layers suspended advantageously in a unitary common carrier and deployed directly onto a porous or fibrous substrate.
Electroluminescent lighting has been known in the art for many years as a source of light weight and relatively low power illumination. Because of these attributes, electroluminescent lamps are in common use today providing light for displays in, for example, automobiles, airplanes, watches, and laptop computers. One such use of electroluminescence is providing the back light necessary to view Liquid Crystal Displays (LCD).
Electroluminescent lamps may typically be characterized as xe2x80x9clossyxe2x80x9d parallel plate capacitors of a layered construction. Electroluminescent lamps of the current art generally comprise a dielectric layer and a luminescent layer separating two electrodes, at least one of which is translucent to allow light emitted from the luminescent layer to pass through. The dielectric layer enables the lamp""s capacitive properties. The luminescent layer is energized by a suitable power-supply, typically about 115 volts AC oscillating at about 400 Hz, which may advantageously be provided by an inverter powered by a dry cell battery. Electroluminescent lamps are known, however, to operate in voltage ranges of 60 V-500 V AC, and in oscillation ranges of 60 Hz-2.5 KHz.
It is standard in the art for the translucent electrode to consist of a polyester film xe2x80x9csputteredxe2x80x9d with indium-tin-oxide (ITO). Typically, the use of the polyester film sputtered with ITO provides a serviceable translucent material with suitable conductive properties for use as an electrode.
A disadvantage of the use of this polyester film method is that the final shape and size of the electroluminescent lamp is dictated greatly by the size and shape of manufacturable polyester films sputtered with ITO. Further, a design factor in the use of ITO sputtered films is the need to balance the desired size of electroluminescent area with the electrical resistance (and hence light/power loss) caused by the ITO film required to service that area. Generally, a large electroluminescent layer will require a low resistance ITO film to maintain manageable power consumption. Thus, the ITO sputtered films must be manufactured to meet the requirements of the particular lamps they will be used in. This greatly complicates the lamp production process, adding lead times for customized ITO sputtered films and placing general restrictions on the size and shape of the lamps that may be produced. Moreover, the use of ITO sputtered films tends to increase manufacturing costs for electroluminescent lamps of nonstandard shape.
The other layers found in electroluminescent lamps in the art are suspended in a variety of diverse carrier compounds (often also referred to as xe2x80x9cvehiclesxe2x80x9d) that typically differ chemically from one another. As will be described, the superimposition of these carrier compounds upon one another and on to the sputtered ITO polyester film creates special problems in the manufacture and performance of the lamp.
The electroluminescent layer typically comprises an electroluminescent grade phosphor suspended in a cellulose-based resin in liquid form. In many manufacturing processes, this suspension is applied over the sputtered ITO layer on the polyester of the translucent electrode. Individual grains of the electroluminescent grade phosphor are typically of relatively large dimensions so as to provide phosphor particles of sufficient size to luminesce strongly. This particle size, however, tends to cause the suspension to be non-uniform. Additionally, the relatively large particulate size of the phosphor can cause the light emitted from the electroluminescent to appear grainy.
The dielectric layer typically comprises a titanium dioxide and barium-titanate mixture suspended in a cellulose-based resin, also in liquid form. Continuing the exemplary manufacturing process described above, this suspension is typically applied over the electroluminescent layer. It should be noted that for better luminescence, the electroluminescent layer generally separates the translucent electrode and the dielectric layer, although those in the art will understand that this is not a requirement for a functional electroluminescent lamp. It is possible that unusual design criteria may require the dielectric layer to separate the electroluminescent layer and the translucent electrode. It should also be noted that, occasionally, both the phosphor and dielectric layers of the lamps in the art utilize a polyester-based resin for the carrier compound, rather than the more typical cellulose-based resin discussed above.
The second electrode is normally opaque and comprises a conductor, such as silver and/or graphite, typically suspended in an acrylic or polyester carrier.
A disadvantage of the use of these liquid-based carrier compounds standard in the art is that the relative weight of the various suspended elements causes rapid separation of the suspension. This requires the frequent agitation of the liquid solution to maintain the suspension. This agitation requirement adds a manufacturing step and a variable to suspension quality. Furthermore, liquid carrier compounds standard in the art tend to be highly volatile and typically give off noxious or hazardous fumes. As a result, the current manufacturing process must expect evaporative losses in an environment requiring heightened attention to worker safety.
A further disadvantage in combining different carrier compounds, as is common in the art, is that the bonds and transitions between the multiple layers are inherently radical. These radical transitions between layers tend strongly to de-laminate upon flexing of the assembly or upon exposure to extreme temperature variations.
A still further disadvantage in combining different carrier compounds is that different handling and application requirements are created for each layer. It will be appreciated that each layer of the electroluminescent lamp must be formed using different techniques including compound preparation, application, and curing techniques. This diversity in manufacturing techniques complicates the manufacturing process and thus affects manufacturing cost and product performance.
A need in the art therefore exists for an electroluminescent system in which the layers are suspended in a unitary common carrier. A structure would thereby be created in which, once cured, layers will become strata in a monolithic mass. Manufacturing will thus tend to be simplified and product performance will tend to improve.
The present invention addresses the above-described problems of electroluminescent lamps standard in the art by suspending layers, prior to application, in a unitary carrier compound, advantageously a vinyl resin in gel form. Once cured, the unitary carrier compound thus effectively bonds each individually applied layer into a stratified monolithic mass. As a result, electroluminescent lamps made in accordance with the present invention are stronger, and less prone to de-lamination. Also, manufacturing is simplified.
As noted, a preferred embodiment of the present invention uses a vinyl resin in gel form as the unitary carrier compound. This choice of carrier is surprisingly contrary to the expected teachings of the prior art. As noted above, a functional electroluminescent lamp requires a dielectric layer to enable capacitive properties. Vinyl resin is not commonly used as a dielectric material and, thus, its utilization is counter intuitive. This choice of carrier has further, and somewhat serendipitously, proven to be compatible with a wide variety of substrates, including metals, plastics and cloth fabrics. Moreover, unlike traditional carrier compounds, vinyl gel is highly compatible with well-known manufacturing techniques such as silk-screen layer printing.
A preferred application of the presently preferred embodiment is in the apparel industry. It will be readily appreciated that the electroluminescent system as disclosed herein may be applied by conventional silk-screening techniques to a very wide range of garments and attire, so as to create electroluminescent designs of virtually limitless shape, size and scope. This application should be distinguished from apparel techniques previously known in the art where pre-manufactured electroluminescent lamps of predetermined shape and size were combined and affixed to apparel by sewing, adhesive, or other similar means. It will be understood that the present invention distinguishes clearly from such techniques in that, unlike prior systems, the fabric of the apparel is used as the substrate for the electroluminescent system.
It will also be understood that the present invention is expressly not limited to apparel applications. As noted, the present invention is compatible with a very wide range of substrates and thus has countless further applications, including, but not limited to, emergency lighting, instrumentation lighting, LCD back lighting, information displays, backlit keyboards, etc. In fact, the scope of this invention suggests strongly that in any application where, in the past, information or visual designs have been communicable by ink applied to a substrate, such applications may now be adapted to have that same information enhanced or replaced by electroluminescence.
It will be further appreciated that accessories standard in the art may be combined with the present invention to widen yet further the scope of applications thereof. For example, dyes and/or filters may be applied to obtain virtually any color. Alternatively, timers or sequencers may be applied to the power supply to obtain delays or other temporal effects.
It will be further appreciated that, while a preferred embodiment of the present invention involves application by silk-screen printing techniques, any number of application methods will be suitable. For example, individual layers may alternatively be applied to a substrate by spraying under force from a nozzle not in contact with the substrate. It should be further noted that, according to the present invention, each of the layers comprising the electroluminescent system of the present invention may even be applied in a fashion different from its neighbor.
A technical advantage of the present invention is that, although applied serially, layers of the present invention bond inherently strongly to their neighbors because of the use of a unitary carrier compound. This bonding of each layer enables a stratified monolithic mass. The monolithic structure of the present invention will then tend not to de-laminate upon flexing as has been found to be a disadvantage with current systems.
A further technical advantage of the present invention is that by using a unitary carrier compound for multiple layers, manufacturing tends to be simplified and manufacturing costs will be inevitably reduced. Only one carrier compound need be purchased and handled in a preferred embodiment of the present invention. Furthermore, layer application and materials handling, including equipment cleanup, is simplified, since each layer may be applied by a like process, will require similar conditions to cure, and is cleanable with the same solvents.
A still further technical advantage of the present invention when utilizing a vinyl resin in gel form as the carrier is that the gel maintains continued full suspension of the active ingredients long after the initial mixing thereof. It will be understood that such maintained suspension results in savings in manufacturing costs because the ingredients tend not to settle out of the suspension, eliminating the need for re-agitation.
Furthermore, a gel carrier tends to reduce spoilage, since gels are less volatile than carrier compounds used traditionally in the art. Spoilage is reduced further by the increased suspension life as described above. The requirement in the art for frequent agitation of volatile carrier compounds tends to encourage evaporation of the carrier compounds. By eliminating the need for frequent agitation, less carrier compound will tend to evaporate.
A further technical advantage of the present invention is realized by using admixtures in the electroluminescent layer whose particulate structure is smaller than the encapsulated electroluminescent grade phosphor also suspended therein. The addition of such admixtures result in a more uniform application of the electroluminescent layer. Such admixtures also tend to act as an optical diffuser that remediates the grainy effect of the phosphor""s luminescence. Finally, experimentation suggests that such admixtures may even cooperate with phosphor at the molecular level to enhance the luminescence of the encapsulated phosphor itself.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.